1. Field of the Invention
The present invention is directed to the field of radiodiagnostic agents and more particularly to scintigraphic agents.
2. Description of the Prior Art
Aqueous suspensions of various metallic hydroxides such as Fe(OH).sub.2, Fe(OH).sub.3 and Sn(OH).sub.2 tagged with a radionuclide such as technetium-99m have been used to obtain perfusion lung scintigraphs which provide significant diagnostic information describing circulatory defects within the lungs. Suspensions used for lung scintigraphy must be tagged with a short lived gamma-emitting radionuclide and also be within a prescribed size range distribution. Pulmonary lung scintigraphy is based upon physical entrapment of radioactive particles within the capillary and terminal arterial network of the lungs. The anatomy of the pulmonary system requires that the particles be greater than 10.mu. in diameter in order for entrapment to occur but particles greater than 100.mu. are to be avoided because they would tend to occlude major arterioles and thus present a potential hazard.
Metallic hydroxide suspensions for this purpose have previously been prepared by admixing an aqueous solution containing a hydrolyzable salt of the metal and a compound of the radionuclide with a solution of a strong base such as sodium hydroxide under carefully controlled conditions. The precipitated metal hydroxide thereby acts as a collector and carrier for the radionuclide. Even under the most carefully controlled conditions, this method yields at best a suspension of irregularly shaped particles, a significant percentage of which are generally either too small or too large. There has been an unfulfilled need, therefore, for an improved method for preparing metallic hydroxide suspensions containing particles which are substantially spherical and which have diameters within the desired range of 10.mu. and 100.mu..